The phenomenon of muscle migration in growing bones is of great importance to developmental and evolutionary biology and to orthopedics; yet it is only poorly understood. The objective of the proposed research is the acquisition of accurate and more complete data describing this process and experimental results pointing to the clarification of the factors controlling migration. The methods will involve cross-sectional and longitudinal studies of migration in a variety of species, including both normal and abnormal growth states, and experimental surgical procedures designed to isolate the control factors.